If someone had told Camila Vallejo during the student uprisings in 2011 that she and her fellow student leaders would end up as elected members of congress, she would have emphatically disagreed. "I would have said you are crazy!" she told the Observer last week.

But polls show that three former student activists are poised to win congressional seats on Sunday, as Chileans head to vote in presidential and congressional elections.

The former Chilean president Michelle Bachelet, a socialist paediatrician and former political prisoner who was tortured during the Pinochet dictatorship, heads the New Majority coalition and is expected to easily win the presidential race. Even if Bachelet receives less than 50% in the crowded nine-candidate field, she will be the overwhelming favourite to triumph in the 15 December runoff. Bachelet's main opponent, Evelyn Matthei, is the daughter of a pro-Pinochet military leader and her extreme-right views are finding little resonance with Chile's increasingly progressive electorate.

"The rightwing is in intensive care. You can see it in the polls and in the streets," said Vallejo, the 25-year-old former student leader. "They are unleashing pure propaganda. It's an attempt to salvage the low turnout they maintain. It's sad … they could have taken the high road and had a serious debate and a discussion about political platforms."

Inspired by the 2011 student uprising, social movements in Chile have poured into the streets, formed hundreds of community organisations and used social networks including Facebook and Twitter to organise strikes and upend Chile's traditionally conservative political agenda.

Vallejo said the student movement was key in breaking "the cultural hegemony of the neoliberal model imposed on Chile during the military dictatorship".

Though the Pinochet dictatorship ended 23 years ago, many of the institutional pillars of Chilean politics – including the 1980 constitution – maintain key tenets of Pinochet's radical free-market "Chicago Boys" strategy. While economic growth in Chile over the past quarter century has been phenomenally stable – often topping 5% a year – key social institutions including public health, education and prisons are widely seen as failures. An invigorated populace is now demanding a radical overhaul of Chile's market-oriented ideology.

Karol Cariola, a 26-year-old nurse who organised student protests in 2011, said: "Our country has started to live a new [political] era … As youth and student leaders we were the protagonists. We are part of this social movement that shook up and awoke this country. It is necessary that we arrive in congress to shake up a congress that has been tremendously hermetic and conservative."

Asked about the agenda for the young leaders, Cariola cited free university education, tax reform, a full overhaul of the Pinochet-era constitution and reform of election laws that are tailored to protect pro-Pinochet rightwing political parties. A recent change in election procedures allows all adult Chileans to vote rather than the system in which only registered adults were eligible.

While polls show apathy among younger Chileans, the presence of former student leaders on the ballot has ignited a wave of enthusiasm in certain districts that is expected to bring at least three, possibly five, former student leaders into power. Vallejo, Cariola [both supported by the Chilean Communist party] and independent student leader Giorgio Jackson are all expected to take seats in congress. Union activists and community organisers are also campaigning to convert their street leadership roles into seats in the Chilean congress.

Chilean senator Víctor Pérez, of the rightwing UDI party, is opposed to these political forces. Pérez called on party loyalists to defend what he called the "Christian values" that have allowed Chile to develop "a moral and ethical model which has allowed us to have an orderly society … and that are at risk by a leftist government that promotes abortion and same-sex marriages".

Pérez argued that the priority of the Chilean state was "the protection and promotion of the family, which is formed when a man and a woman opt for a common life and have children, that is not possible with same-sex couples". He described marriage as "an institution designed to form families".

Despite Pérez's call to protect traditional "Christian" values, Chile's most traditional group known as La Familiar Militar (The Military Family) feels betrayed by the rightwing and has organised a boycott of the elections. "You have abandoned us, handed us over to the stateless vengeance of defeated leftists," said Lisandro Contreras, national co-ordinator for Plan Now, an organisation of pro-Pinochet military supporters. "It is no longer possible to support the political/judicial persecution. We can no longer stupidly believe in the [current government] of [Sebastián] Piñera."

The former Pinochet officials are incensed that the current centre-right government of Pinera did not issue pardons for human rights crimes and by Piñera's decision to shut down special "country club" prisons for military officials charged with murder, kidnapping and torture during the 17-year military dictatorship. The Plan Now webpage now opens with a call for Chilean military members and their families to punish rightwing parties. "Don't vote this 17 November," the red-lettered message states. "Show the politicians that betrayal has a price."

Bachelet, who supports gay marriage and abortion and has promised free daycare centres nationwide, is expected to win easily. Governing the now-enervated Chilean electorate, however, requires both acknowledging the need for change and tempering the pace of reform. "There is this very successful country that we see in the news, but that is not always what we see in our own homes," said Bachelet during her final campaign rally last Thursday.

She called on supporters to "confront the inequality" and vote for the New Majority coalition that she heads. "We have to vote for a new constitution that is much more than a text," said Bachelet, who recognised the difficulties of pushing her agenda through a congressional system still ruled by arcane procedures from the Pinochet dictatorship. "Some changes we can complete, others we will launch," she said.

She called on citizens to vote for those "who measure up to the challenges" now facing Chile's political leaders.

Those challenges were starkly outlined by the results of Chilean student elections held last week, that brought forth a notably more radical student leadership. "I don't vote," said Melissa Sepúlveda, the newly elected president of the politically powerful University of Chile student union.

Sepúlveda, a fourth-year medical student, said she would not vote for Bachelet or the former student leaders and declared: "I identify with the history of the anarchist movement", which she described as dedicated not to violence but to "direct democracy".

"The bloc or coalition in power continues to be those – who since the dictatorship – have consolidated the neoliberal model in Chile," said Sepúlveda. "I think the possibilities for change are based in organisations and the force that they can exert."